You will be able to remove the closing tags easily enough as they will all be the same. e.g. [/font], [/color].
For the opening tags however you will either need a different query for each specific font and color, which could be a lot depending on how many different ones there are.
Or you can use regex to catch them all with one string.
FWIW, I did exactly the same with my phpBB forum, removing redundant BB Code before importing.